The older non-imaging concentrator devices comprise either truncated axi-symmetrical cones of revolution with reflecting metallic shells, or truncated axi-symmetrical cones in glass. In both cases, the input area is greater than the output area, and the acceptance angle of the light rays at the input is smaller than the emergence angle at the output. Concentrators of the second type have been improved from the concentration standpoint, by replacing the truncated cone by a truncated axi-symmetrical paraboloid, and by combining in series truncated cones and truncated paraboloids, each element being constituted by a homogeneous and transparent block in a material having the same refraction index, but said index being able to vary from one element to another. Truncated cones constituted by layers of materials having indexes increasing from the input to the output, perpendicularly to the axis of the cone, have also been tried.
The illumination obtained in output is quasiuniform throughout the entire surface. The receiver can therefore be easily installed at the output of the concentrator.
But with these non-imaging concentrators, it is also necessary to follow the source if the latter moves, yet with less accuracy than in the preceding case.
The theoretical maximum concentration is given by the equation (CLAUSIUS principle): EQU C=(n'Sin U'/nSin U).sup.2
in which n and n' are respectively, the refraction indices of the truncated cone (or truncated paraboloid) and of the output medium; U and U' are, respectively, the cone apex half angles, of acceptance in the truncated cones, and of emergence in the output medium.
Concentration is low and so is the acceptance angle. For example, for the truncated cone, concentration is about 2 for n=1.5 with a solid acceptance angle of about one sixth of a Steradian. The solid emergence angle, on the contrary, is high, nearly 2 .pi. Steradian in the air, this necessitating an adaptation of the indices of the truncated cone and of the receiver (immersion in a liquid).
To adjoin lenses at the input and at the output of a truncated cone (or truncated paraboloid) makes it possible to considerably increase concentration and to reduce the emergence angle, but reducing accordingly the acceptance angle, which is but a few hundredths of a Steradian (Malifaud 1964).
The aforementioned theoretical maximum concentrations are nowhere near what is obtained with these devices, as this pre-supposes the use of faultless components and a perfect alignment in the source direction.
It is the object of the present invention to regroup all the advantages of the two already existing systems mentioned hereinabove, leaving out all the disadvantages, and to reach a high concentration without any limitation of directivity.
And the invention proposes to this effect a multidirectional non-imaging radiations concentrator and/or deconcentrator device which comprises, like the known concentrator truncated cones with reflecting surface or transparent block, in extension of a radiation conductor of constant cross-section, a radiations-confining interface of truncated shape, of which the directrices and generatrices can be any type.
Moreover, U.S. Pat. No. 4,076,378 describes a device for transmitting image points of variable and controlled spacing. Said device comprises truncated fibers controlling with accuracy the input and output spacings between image points by stacking their thinner ends and their widened ends. Each fiber comprises three layers, of different refraction indices, decreasing from the center towards the periphery so that the light is reflected, in the thinner part of the length, onto the peripheral interface, and in the widened part of its length, onto the central interface of reduced cross-section, said central transmission zone being surrounded by an optically inactive zone extending between the two interfaces. This device is therefore a light transmitter working in two directions between the thinner end and the widened end, but without concentration or deconcentration of energy.
The concentrator and/or deconcentrator device according to the invention also uses two interfaces, but to confine the radiations differently and to propagate them indifferently in one direction or in the other, in order to obtain a concentration or deconcentration of energy, and in some cases, to obtain both simultaneously.
According to the invention, the device comprises at least a second radiations-confining interface of conical shape situated inside the first interface, the distance between these two radiations-confining interfaces being substantially constant, and said two interfaces facing in such a way that the radiations are confined between them and propagate towards or from the widened end of the interface opposite the conductor.
With such an improved device, it is possible to obtain a high acceptance angle, capable of reaching as much as the whole of the frontal half-space. This property makes it possible to concentrate the punctual sources (specific light source) as well as the diffuse sources (general ambient background light) and to use the concentrator in a readily choosable fixed position.
In addition, the illumination is uniform in output whatever the source or sources.
Also the concentration is high, theoretically unlimited for a given configuration since it is only dependent on the ratio of the input and output surfaces, or by placing several systems in series.
Such elementary structures with two confining interfaces may be coupled:
in parallel, the first interface of a structure being contiguous to the second interface of the structure surrounding it, and all first interfaces being connected with the same radiation conductor,
or in series, the conductor of one being connected with the widened end of the other,
or else, both in series and in parallel.